Transposons are a powerful tool in molecular biology and genetic research. They are broadly used in bacteria, plants, and invertebrates for mutagenesis, preparation of transgenic individuals, and such. On the other hand, the development of such techniques in vertebrates has been slow. In recent years, a synthetic transposon system called “Sleeping Beauty” has been constructed by connecting Tc1-like transposon fragments, which were discovered in salmonid fish (Ivics, Z., Hackett, P. B., Plasterk, R. H., & Izsvak, Z. Cell 91, 501-510 (1997)). The transposition of this transposon has also been confirmed in mouse embryonic stem cells and germ cell lines, etc. (Luo, G., Ivics, Z., Izsvak, Z. & Bradley, A. Proc. Natl. Acad. Sci. USA 95, 10769-10773 (1998); Yant, S. R., Meuse, L., Chiu, W., Ivics, Z., Izsvak, Z. & Kay, M. A. Nat. Genet. 25: 35-41 (2000); Fischer, S. E., Wienholds, E. & Plasterk, R. H. Proc. Natl. Acad. Sci. USA 98: 6759-6764 (2001); Horie. K., Kuroiwa, A., Ikawa, M., Okabe, M., Kondoh, G., Matsuda, Y. & Takeda, J. Proc. Natl. Acad. Sci. USA 98, 9191-9196 (2001); Dupuy, A. J. Fritz, S. & Largaespada, D. A. Genesis 30: 82-88 (2001)).
While “Sleeping Beauty” is a synthetic transposon, an active natural transposon has also been discovered in vertebrates. This transposon, Tol2, is the only natural transposon in vertebrates, and was cloned from the medaka fish (killifish) genome (Koga, A., Suzuki, M., Inagaki, H., Bessho, Y., & Hori, H. Nature 383, 30 (1996)). Since the Tol2 sequence is analogous to that of the Ac element in maize, it has been classified into the hAT family of transposons. Furthermore, the transposition of this Tol2 has not only been observed in medaka fish embryos (Koga, A., & Hori, H. Genetics 156, 1243-1247 (2000)), but also in the germ line of zebrafish (Kawakami, K., Koga, A., Hori, H., & Shima, A. Gene 225, 17-22 (1998); Kawakami, K., & Shima, A. Gene 240, 239-244 (1999); Kawakami, K., Shima, A., & Kawakami, N. Proc. Natl. Acad. Sci. USA 97, 11403-11408 (2000)). However, it has not been found in mammals.
Such transposons are expected to become extremely useful in both forward genetics, wherein genetic analysis is based on the phenotype of mammalian cells after mutagenesis, and reverse genetics, wherein phenotype analysis is based on genes introduced during preparation of transgenic individuals and such.